The invention relates to an electrodeless discharge lamp comprising a lamp vessel which is sealed in a vacuum-tight manner and is filled with mercury and a rare gas and more particularly to such a lamp having a core of magnetic material in which a high-frequency magnetic field can be induced by an electronic ballast, and a coil wound around the core, to produce an electric discharge in the lamp vessel. A holder with an amalgam is disposed in the lamp vessel to act as a mercury vapor source. Such a lamp is known from the British published patent application No. 2,039,138 A.
In the lamp described in this published patent application, the amalgam is located at a comparatively cool area in the lamp vessel, in order to stabilize the mercury vapor pressure at a value of approximately 1 Pa during operation of the lamp. At a mercury vapor pressure of approximately 1 Pa, the conversion of electric energy into ultraviolet radiation (mainly resonance radiation of mercury having a wavelength of 254 nm) is optimized. The amalgam in this known lamp is preferably provided in a holder which is located in the exhaust tube of the lamp vessel.
One of the problems which arise in an electrodeless lamp, especially in such a lamp whose lamp vessel is provided with an amalgam regulating the mercury vapor pressure, is that especially after starting a comparatively long period of time elapses before the correct optimum vapor pressure is reached. Of course, the light output during this time is adversely affected.